BIOLOGY Assertion (A) & Reason (B) MCQ

3. Assertion is true but reason is false.

Explanation:

In mammals, the presence of a Y chromosome is required for the development of a male sex phenotype. ln contrast, the Y chromosome plays no significant role in sex determination in Drosophila. A Y chromosome is required for maleness, moreover, the presence of a single Y chromosome is sufficient even in the presence of several X chromosomes (e.g., XXXXY)

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

Abnormal chromosomal behaviour in insects can result in the formation of gynandromorphs or sexual mosaics in which some parts of the animal are female and other parts are male. Some gynandromorphs in Drosophila are bilateral intersex. Bilateral gynandromorphs have been explained on the basis of an irregularity in mitosis at the first cleavage of the zygote. Infrequently a chromosome lags in division and does not arrive at the pole in time to be included in the reconstructed nucleus. When one of the X chromosomes of an XX (female) zygote lags in the spindle, one daughter nucleus receives two X chromosomes. A mosaic body pattern is thus established. One nucleus in the nuclei stage would be XX (female) and one would be XO (male).

4. Both assertion and reason are false.

Explanation:

Linked genes are those genes which occurs on the same chromosome while unlinked genes are the ones found on different chromosomes. Linked gene show dihybrid ratio of 3 : 1. Linked genes do not show independent assortment.

2. Both assertion and reason are true but reason is not the correct explanation of assertion.

Explanation:

Complementary genes are those non-allelic genes which independently show a similar effect but produces a new trait when present together in the dominant form. W. Bateson and R.C. Pun nett observed that, when two white flowered varieties of sweet pea, Lathyrus odoratus were crossed, F₁ progeny had coloured flowers. When F₂ progeny obtained from F₁ was classified, plants with coloured flowers and those with white flowers were obtained in 9 : 7 ratio. The two dominants are brought together in F1 generation and therefore coloured flowers are produced.

2. If both the assertion and reason are true but the reason is not a correct explanation of the assertion.

Explanation:

Phenylketonuria is due to deficency of liver enzyme Phenyanaline hydroxylase which converts phenylanine into tryosine.

It occurs in person who are homozygous recessive.

It results with a high level of phenylalanine in blood, tissue fluids and urine.

Therefore both assertion and reason is true.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

According to Mendel's concept ofinheritance, each gene had two alternative forms or allelomorphs, one being dominant and the other recessive. Practically, the wild form can mutate in several ways. The mutant form can also mutate once again to give rise to another mutant form. Therefore, a gene can have more than two allelomorphs. These allelomorphs make a series of multiple alleles.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

Mutations are sudden unpredictable inheritable departures from the normal type without any intermediate stage. Discontinuous variations form the basis of mutation theory of evolution which was proposed by De Vries (1902).

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

Back cross is a cross which is performed between hybrid and one of its parents. In plant breeding, back cross is performed a few times in order to increase the traits of that parent. for example, a crop plant is crossed with a wild variety in order to obtain its disease resistance. In the process, most good traits of the crop plant get diluted. The hybrid is, therefore, repeatedly crossed with parent crop plant in order to transfer the good traits back into it.

2. Both assertion and reason are true but reason is not the correct explanation of assertion.

Explanation:

Karyotype is the chromosome complement of a cell, individual or group of similar individuals that provides description of number, types and other characteristics of chromosomes. Any change in the chromosome number is detected immediately. Chromosomal aberrations or abnormalities are found about. This chromosome technique has made it possible to know the sex of developing fetus by drawing amniotic fluid and preparing karyotypes from cells derived from fetus floating in this fluid.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

The gene which inhibits or suppresses the expression of a non-allelic gene is known as epistatic gene. Epistasis reduces the number of phenotypes appearing in the F₂ generation of dihybrid cross. Thus instead of normal 9 : 3 : 3 : 1 dihybrid ratio, epistasis may result in a ratio of 9 : 3 : 4 (recessive epistasis). 12 : 3 : 1 (dominant epistasis). 13 : 3 (dominant recessive epistasis) or 9 : 7 (double recessive epistasis), etc

2. Both assertion and reason are true, but reason is not the correct explanation of assertion.

Explanation:

Linkage group is linearly arranged groups of genes which fail to show independent assortment as these are present on the same chromosomes.

4. Both Assertion and Reason are incorrect.

Explanation:

Chromosomal determination of sex is based on heterogamety or occurrence of two types of gamete in one of the two sexes.

In Drosophila XX - XY type of sex determination is found where males are heterogametic. 

In moths, ZO - ZZ type of sex determination occurs where males are homogametic. 

3. Assertion is true but reason is false.

Explanation:

Monohybrid cross is a cross between two organisms of a species which is made to study the inheritance of a single pair of alleles or factors of a character. Dominant character is one of a pair of alleles which can express itself whether present in homozygous or heterozygous state. ln F₁ generation, (the generation of hybrids produced from a cross between the genetically different homozygous individuals called parents) the progenies are heterozygous dominant.

2. Both assertion and reason are true but reason is not the correct explanation of assertion.

Explanation:

In birds, chromosomal composition of the egg determines the sex. This is called genetic sex determination, with females being heterogametic. But being heterogametic is alone not responsible for sex determination. Other factors like specific genes or autosomal, sex chromosome ratio, etc., are responsible.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

Haplodiploidy is a type of sex determination in which the male is haploid while the female is diploid. It occur in some insects like bees, ants and wasps. Male insects are haploid because they develop parthenogeneticlly from unfertilised eggs. Meiosis does not occur from fertilised eggs and hence diploid.

3. Assertion is true but reason is false.

Explanation:

Since, in hybrids probability of dominant traits to come together increases. They are generally better than parents but this is not always true and not all dominant traits come in all the hybrids.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

Quantitative inheritance is a type of inheritance controlled by one or more genes in which the dominant alleles have cumulative effect with each dominant allele expressing a part or unit of the trait, the full trait being shown only when all the dominant alleles are present. The genes involved in quantitative inheritance are called polygenes. A polygene is defined as a gene where a dominant allele controls only a unit or partial quantitative expression of a trait.

2. Both assertion and reason are true but reason is not the correct explanation of assertion.

Explanation:

Pure line is a strain of genetically pure true breeding individuals. Members of pure line are homozygous for one or more characters. ln homozygous form both the factors express the same effect. These organisms are said to breed true. They are used for cross breeding in order to get the desired improvement in crops.

4. If both the assertion and reason are false.

Explanation:

Plasmids are extrachromosomal double stranded small circular DNA usually found in bacterial cell in addition to main genetic material. Therefore, both assertion and reason is false.

1. Both assertion and reason are true and reason is the correct explanation of assertion

Explanation:

Backcross is cross which is performed between hybrid and one of its parents. ln test cross, the individual is crossed with recessive parent. It is called a test cross, because it is used to test whether an individual is homozygous or heterozygous (hybrid).

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

According to principle of segregation (first law of Mendelism), the two factors of a character which remain together in an individual do not get mixed up but keep their identity distinct, separate at the time of gametogenesis or sporogenesis, get randomly distributed to different offspring as per the principle of probability. Gametes carry a single factor or allele for a trait. The two Mendelian factors present in the F₁ plants segregate during gamete formation. The principle of segregation is called the principle of purity of gametes because segregation of the two Mendelian factors of a trait results in gametes receiving only one factor out of a pair. As a result gametes are always pure for a character.

2. Both assertion and reason are true but reason is not the correct explanation of assertion

Explanation:

Mendel chose garden pea as plant material for his experiments, since it had the following advantages:

• Well defined characters.
• Bisexual flowers.
• Predominantly self-fertilisation.
• Easy hybridisation.

Garden pea having following characteristics proved a very good experimental material. But it was not the only reason for Mendel's success. Main reason was preparation and selection of pure lines by own work and proper statistical analysis of large number of samples, of one character at a time